The present invention relates to a semiconductor memory device and a method for fabrication thereof, in which a bit line and a storage node are overlapped to improve the integration degree.
FIGS. 1(a) through (d) show cross-sectional views of a device at various stages of a fabrication process according to the prior art.
First, as shown in FIG. 1 (a), a gate 2, a source and drain region 3 and an oxide film 4 are successively formed on a semiconductor substrate 1.
As shown in FIG. 1(b), a bit line contact is formed and a bit line 5 which is either a refractory metal or a silicide and an oxide film 6 are deposited and then patterned to restrict the fixed portion.
As shown in FIG. 1(c), a side wall 7 of the oxide film is formed at both sides of the oxide film 6 and the bit line 5.
As shown in FIG. 1(d), a capacitor consisting of a storage node 8, a dielectric film 9 and a plate 10 is formed, thereby completing fabrication of the prior semiconductor memory device.
However, in semiconductor memory devices fabricated by aforesaid conventional method, as shown in FIG. 2, bit line 5 and storage node 8 are separated in the three dimensions and the active region(AR) is diagonally aligned against the word line 2 and the bit line 5. Therefore, the area of a unit cell is increased and distortion is caused by the bent portion of the active region(AR) generated in processing.